//The second parameter to setState() is an optional callback function that will be executed once setState is completed and the component is re-rendered.
//Generally we recommend using componentDidUpdate() for such logic instead.
//setState()的第二个参数是一个可选的回调函数，它将在setState完成并重新呈现组件时执行。通常，我们建议使用componentDidUpdate()来代替这种逻辑

/*
setState(stateChange[, callback])
*/

//注意：该回调 即使shouldComponent返回false时, 即组件不刷新时, 也会执行
